Data in a distributed database system is stored across a multitude of physically and/or logically distinct nodes. For example, data in a distributed database system may be stored on different computers. Alternately or additionally, data in a distributed database system may be managed by separate processes. As such, a query on data stored in a distributed database is typically executed in sequential phases. For instance, an initial phase for executing the query can include generating, at a global scheduler node, an execution plan for fulfilling the query. Fragments of the execution plan can be distributed to one or more local scheduler nodes that further assign the tasks specified in the plan fragments to the appropriate worker nodes. Meanwhile, during a subsequent phase, one or more worker nodes may perform the tasks assigned to each worker node. In both instances, the nodes (e.g., scheduler and worker nodes) that are involved in the execution of the query can exchange messages (e.g., control messages) in order to coordinate the execution of the query pursuant to the execution plan.